The Hopkins Population Center was established to facilitate population research in various divisions and departments of the University. It consists of five units: a Directorate, Information Unit, a Data Processing Unit, a Mathematical/Statistical Unit and an Electron Microscopy Laboratory. The Center has no research program of its own, its aim rather being to enrich the population research environment, to bring investigators with common interests into contact and to provide research facilities which help in the formulation and conduct of research investigations. The research environment fostered by the center is unusual in the degree of interaction among scientists from different specialties. Sometimes this is reflected in the problems which are selected for study; sometimes in the style of research. As one would expect, however, much of the research in which the Center is involved also arises out of problems particular to special disciplines. The overall effort however is a multifaceted attack on a wide range of problems related to human fertility.